1. Field of the Invention
The present invention relates in general to an image capturing apparatus and an automatic exposure control correcting method. More specifically, the invention relates to an automatic exposure control correcting method for obtaining correct exposure by complementing an automatic exposure adjusting function of an electronic image capturing apparatus, such as an electronic still camera and a video camera, that converts an optical image into electronic image signals with an imaging device and the image capturing apparatus for use in this method.
2. Description of Related Art
An electronic image capturing apparatus or an electronic camera that converts an optical image into electronic image signals by an imaging device such as a charge-coupled device (CCD) image sensor has an automatic exposure adjusting function (AE function) for automatically adjusting a diaphragm and a shutter according to a photometry value and automatically controlling the time in which electric charges are stored in the CCD image sensor. An image captured by the electronic camera with an exposure adjusted by the AE function often has lower image quality than a silver halide photograph. The main subject as well as the background can be blackened or partially whitened. This is because an acceptable dynamic range of the imaging device is much narrower than a silver halide film, and thus, the incorrectness of the AE severely affects the image quality in the electronic image capturing.
To improve the AE performance in the conventional cameras, a screen is divided into a plurality of areas, a scene is identified according to a differences in luminance between the center and the adjacent areas, and the AE is determined according to the identification. Even if the AE is excellent, however, it is difficult to obtain correct exposure for a subject out of AE pattern. To address this problem, there is proposed a method in which the AE is controlled in real-time. For example, Japanese Patent Provisional Publication No. 7-38801 discloses an image capturing apparatus that produces a histogram of a pixel luminance distribution of a captured image during the image capturing and displays the histogram as well as the captured image on an electronic viewfinder to thereby enable an easy confirmation as to the correctness of the exposure. This image capturing apparatus, however, cannot always obtain a correct exposure for a main subject even if the correctness of the exposure is determined from the entire luminance distribution with reference to the histogram displayed on the electronic viewfinder.
As a result of an experiment, the present inventor confirmed that the conventional AE function causes an error of ±1.5EV when a variety of scenes is imaged. Thus, there is a limitation to the AE performance of the camera.
Japanese Patent Provisional Publication No. 1-193708 discloses an autofocus device in a camera that displays an image captured by an imaging device on a liquid crystal display (LCD) part provided with a touch panel and enlarges the image about a touched position on the LCD part to recapture with the focus adjusted on the touched position. This publication, however, does not mention the AE.